Method for forming laminated circuit board

ABSTRACT

Described are processes for developing laminated circuit boards, as well as the resulting circuit boards themselves. Accordingly, at least two circuit boards at least partially overlap each other, and at least one through-hole is formed in an overlapping region thereof. The through-hole is filled with an electrically-conductive material, forming a through-via that enables the circuit boards to be electrically connected. When a circuit on each circuit board is laid out so that a part thereof reaches a region in which the through-via is to be formed, then that part of the circuit can be electrically connected to the through-via. Thus, portions of the circuits on the circuit boards can be electrically connected to each other via common through-vias to realize an integrated device in which the circuits on the laminated circuit boards function.

TECHNICAL FIELD

The present invention relates to a flexible board on which circuits are formed, and particularly relates to a laminated circuit board in which circuits formed on a plurality of laminated circuit boards are connected to each other and function.

BACKGROUND ART

Printed electronics technology for forming electronic devices using printing techniques has been developed and established as a new industry. This technology is characterized in that a low-temperature process based on a printing technique is used to deposit a wiring material, an organic semiconductor material, and an insulating material, so that an electronic device that has the function of a circuit, a display, a sensor, or the like is formed on a soft and lightweight flexible board such as a plastic film. In addition, no vacuum apparatus or high-temperature device is needed during manufacturing, and thus there is an advantage in that the manufacturing cost is suppressed. In view of low costs and the functionality as being lightweight, soft, and the like, application to various fields and market expansion are expected.

Until now, as essential printed electronics technologies, various technologies including: wiring technology; display devices such as organic EL displays and electronic paper; organic EL lighting; battery technology; electronic device technology such as various types of sensors, and storage elements; and the like have been developed, and many of them have reached the practical level. On the other hand, these technologies are typically applied to a single device, and there has hardly been any effort to integrate various electronic devices on a flexible board. This is mainly attributed to the semiconductor technology.

Organic semiconductors have attracted attention as an important field in printed electronics technology, but a state in which, due to poor performance and material instability, practical use has not been achieved has continued for a long time. Meanwhile, a high-performance and stable organic semiconductor material and a deposition technique thereof have recently been developed, and research and development toward the practical use thereof has gradually gained traction.

In view of the above-described technical background, the possibility of integrating various printable electronic devices on a flexible board so that they operate at a practical level has increased. Hereafter, a technique for efficiently integrating printable electronic devices on a flexible board is desired.

PRIOR ART DOCUMENT Patent Document

-   Patent Document 1: JP 2000-277689A

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

If electronic devices having various functions are integrated on the same board, then the area of the integrated devices will increase and the yield ratio will greatly decrease. The present invention provides a highly productive technique of printable electronic device integration that is needed when a plurality of electronic devices are integrated on a flexible board.

Means for Solving Problem

The present invention is such that electronic devices that are to be integrated are formed on individual boards, and the boards are laid to overlap each other in a predetermined relationship, and then are electrically connected to each other, so as to be able to function as an integrated device.

Specifically, at least two circuit boards on which electronic devices are formed are laid to overlap each other partially or entirely, and at least one through-hole is formed in an overlapping region penetrating the plurality of circuit boards. Furthermore, this through-hole is filled with an electrically-conductive material, and a through-via that enables the circuit boards to be electrically connected is formed. On the other hand, if a circuit on each circuit board is laid out in advance so that a part thereof reaches a region in which the through-via is to be formed, then the part of the circuit can electrically be connected to the through-via. Accordingly, by laying out, in advance, portions of the circuits on the circuit boards that are desired to be connected to each other so that they are connected to the same one of through-vias, it is possible to realize an integrated device in which the circuits on the laminated circuit boards function.

Effects of the Invention

If a plurality of electronic devices are formed sequentially on one flexible board, typically, a yield ratio of each electronic device is multiplied, and therefore the yield ratio of the integrated device decreases. According to the present invention, individual good electronic devices are selected and laminated, and thus the problem that the yield ratio of the integrated device decreases can be prevented. In addition, it is possible to prevent the increase in the area when multiple electronic devices are integrated.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a perspective view illustrating a laminated integrated device 150 according to a first embodiment of the present invention. The laminated integrated device 150 is obtained by laminating circuit boards 110, 120, 130, and 140.

FIG. 1B is a top view of the laminated integrated device 150. Parts of the circuit boards 110 and 130, and the entire upper surface of the circuit board 140 are shown. The circuit board 120 is hidden by the circuit board 130 and cannot viewed. This figure also shows through-vias 301 for electrically connecting the circuit boards.

FIG. 2A is a diagram schematically illustrating a lamination process flow according to the first embodiment of the present invention, showing a situation in which the circuit boards 110, 120, 130, and 140 that are to be laminated are positioned in a predetermined positional relationship.

FIG. 2B is a diagram schematically illustrating the lamination process flow according to the first embodiment of the present invention, showing a state immediately after the laminated circuit boards 110, 120, 130, and 140 have been bonded to each other.

FIG. 2C is a diagram schematically illustrating the lamination process flow according to the first embodiment of the present invention, showing a state in which a plurality of through-holes 201 are formed in the bonded circuit boards at predetermined positions.

FIG. 2D is a diagram schematically illustrating the lamination process flow according to the first embodiment of the present invention, showing a state in which an electrically-conductive material is embedded in the through-holes 201 to form the through-vias 301.

FIG. 3 is a diagram illustrating the laminated integrated device 150 according to the first embodiment of the present invention, showing a region A, which is a region on the laminated integrated device 150, and a direction B along which a cross section of the region A is taken, the region A and the direction B being referenced in the description below.

FIG. 4 illustrates a top view of the region A (upper figure) immediately after the circuit boards 110, 120, 130, and 140 are bonded to each other in the lamination process of the first embodiment of the present invention, and a cross-sectional view of the region A (lower figure) that is taken along B. In the figures, the reference numerals 111, 112, 113, and 114 denote interconnects on the circuit board 110, the reference numerals 121, 122, 123, and 124 denote interconnects on the circuit board 120, the reference numerals 131, 132, 133, and 134 denote interconnects on the circuit board 130, and the reference numerals 141, 142, and 143 denote interconnects on the circuit board 140.

FIG. 5 illustrates a state immediately after the plurality of through-holes 201 are formed in the laminated circuit board obtained by bonding the circuit boards 110, 120, 130, and 140 to each other in the lamination process of the first embodiment of the present invention, with the upper figure showing a top view of the region A, and the lower figure showing a cross-sectional view of the region A taken along B.

FIG. 6 illustrates a state immediately after the electrically-conductive material is embedded in the through-holes 201 and the through-vias 301 are formed in the lamination process of the first embodiment of the present invention, with the upper figure showing a top view of the region A, and the lower figure showing a cross-sectional view of the region A taken along B.

FIG. 7 is a schematic diagram illustrating an example of the present invention in which no through-via is used.

DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Embodiment 1

FIGS. 2A, 2B, 2C, and 2D schematically show the present invention in which circuit boards 110, 120, 130, and 140 are laminated, through-holes 201 are formed at predetermined positions penetrating all of the boards, and an electrically-conductive material is embedded in the through-holes to form through-vias 301 for electrically connecting circuits provided on the circuit boards.

In the present embodiment, four flexible boards are laminated, the four flexible boards including: the board 110 on which illuminance sensors for monitoring illuminance are arranged in a line; the board 140 on which a temperature sensor is formed; and the boards 120 and 130 that are two separate boards on which circuits for controlling the illuminance sensors and the temperature sensor are formed divided between the two. Within the application range of the present invention, the number of boards is not limited.

FIG. 4 shows the four circuit boards immediately after they are bonded to each other, in a partial cross sectional view taken along a line (direction B) intersecting a row of the through-vias that are to be formed in the subsequent process, and in a top view thereof. Interconnects on the circuit boards are laid out in advance so that: in the range shown in this figure, interconnects 111 and 121 are connected to each other; interconnects 131 and 141 are connected to each other; interconnects 112, 122, and 132 are connected to each other; interconnects 113, 123, 133, and 142 are connected to each other; and interconnects 114, 124, 134, and 143 are connected to each other.

Circuits, which are however not shown, on the circuit boards are each made of a plurality of interconnect layers, and only the interconnects of the uppermost layer are shown. Within the application range of the present invention, a layout configuration is possible in which only one circuit interconnect layer is provided on the circuit board, or in which an intermediate layer of multilayer interconnects is connected to a through-via.

FIG. 5 shows a cross sectional view and a top view of a part (region A) of the laminated circuit board immediately after the through-holes 201 are formed, at predetermined positions, in the laminated circuit board obtained by bonding the circuit boards 110, 120, 130, and 140 to each other. In the present embodiment, the through-holes are formed using a laser, but in the application range of the present invention, the means for forming the through-holes is not limited. Furthermore, in the figure, the through-holes are formed through the circuit board 110 of the lowermost layer as well, but the through-holes are not necessarily formed passing through the board of the lowermost layer.

FIG. 6 shows a cross sectional view and a top view of a part (region A) of the laminated circuit board immediately after an electrically-conductive material is embedded in the through-holes 201 formed in the previous step and the through-vias 301 are formed. As a result of the through-vias 301 being formed, the circuits on the circuit boards 110, 120, and 130 are connected to each other at necessary contacts, and all of the laminated boards function as an integrated device.

In the present embodiment, an electroless plating method is used to embed gold to form the through-vias, but within the application range of the present invention, another method may also be used to embed another electrically-conductive material. Furthermore, it is not essential to completely fill the through-holes with an electrically-conductive material. It is also possible to form an electrically-conductive material layer only on side walls of the through-vias using a plating method or the like. It is possible to connect circuits on the circuit boards to each other at necessary positions using an electrically-conductive material in the through-vias, which is an object of the present patent application.

Furthermore, in the present embodiment, the through-vias formed in the through-holes are used to connect the circuits on the circuit boards to each other, but it is also possible to form notch-shaped or semicircular recesses at peripheral ends of the circuit boards, and to bring the electrically-conductive material into contact with the circuit boards along the recesses, so that the circuits on the circuit boards are connected to each other. The recesses may not necessarily be formed if a large contact surface can be ensured between the circuits on the circuit boards and the electrically-conductive material that connects the circuit boards. As a method for ensuring such a large contact surface, it is also advantageous that the circuit boards are laid to overlap each other while being shifted little by little. FIG. 7 is a perspective view schematically showing this state.

Embodiment 2

The forgoing first embodiment has described an example in which four circuit boards are laminated, but as an application of the present invention, it is also possible that, when a plurality of circuit boards are laminated, the circuit boards are bonded to each other while being classified into several groups, through-holes are formed in each group of laminated boards, then these groups of laminated boards are laid to overlap each other, and through-vias are formed. Furthermore, it is also conceivable that the present invention is applied to each group of laminated boards to subject the group of laminated boards to processing until the formation of through-vias, and then the groups of laminated boards are further laminated. In the latter case, all of the positions of the through-vias of the groups of laminated boards are not necessarily aligned, and the groups of laminated boards may be arranged so that only through-vias that need to be connected to each other overlap each other when all of the laminated boards are bonded to each other. This makes it possible for the entire integrated device to function.

Laminated circuit boards to which the present invention was applied are formed in advance. For example, a first laminated circuit board may be obtained by laminating two circuit boards, a second laminated circuit board may be obtained by laminating four circuit boards, and a third laminated circuit board may be obtained by laminating five circuit boards. These laminated circuit boards have through-vias. These through-vias are arranged so as to be connected to each other as appropriate when the three laminated circuit board are stacked together.

A laminated integrated device is obtained by laminating these three laminated boards.

Functions and Effects

The present embodiment relates to an integration of illuminance sensor arrays, a temperature sensor, and an organic semiconductor circuit, but if these are formed on the same flexible board, the area of the integrated devices increases, and thus the yield ratio greatly decreases. In the experiment, the yield ratio never exceeded 20%. When the present invention was applied, it was observed that a yield ratio of about 80% could be achieved. 

The invention claimed is:
 1. A method for forming a laminated circuit board in which a plurality of flexible circuit boards are laminated, each flexible circuit board being provided with a printable electronic device that is formed on a flexible film using a printing technique, wherein an organic semiconductor circuit is formed on at least one of the plurality of flexible circuit boards, the plurality of flexible circuit boards each have at least one side surface and are arranged so that a region in a vicinity of the one side surface of one flexible circuit board among the plurality of flexible circuit boards overlaps a region in a vicinity of the one side surface of at least one other of the plurality of flexible circuit boards, wherein each of the plurality of flexible circuit boards has a top side and a bottom side, and an area of the bottom side of two of the flexible circuit boards is less than an area of the top side of the at least one other flexible circuit board, and electrical connection of the one flexible circuit board with the at least one other flexible circuit board is made via a through-via that is formed in a vicinity of one edge of the one flexible circuit board and a region in a vicinity of the one edge of the at least one other flexible circuit board, or via an electrically-conductive material arranged on the one side surface of the flexible circuit boards.
 2. The method for forming a laminated circuit board according to claim 1, wherein the electrical connection is made by forming at least one through-hole that penetrates the plurality of flexible circuit boards in the vicinity of the one edge of the one flexible circuit board and the region in the vicinity of the one edge of the at least one other flexible circuit board in a state in which the one flexible circuit board and the at least one other flexible circuit board overlap each other, embedding the electrically-conductive material in the through-hole to form the through-via, and laying out in advance circuit interconnects on the circuit boards so that parts of the circuit interconnects reach the vicinity of the one edge of the one flexible circuit board and the region in the vicinity of the one edge of the at least one other flexible circuit board in which the through-via is to be formed.
 3. The method for forming a laminated circuit board according to claim 2, wherein an opening of the through-via increases toward a top layer.
 4. The method for forming a laminated circuit board according to claim 1, wherein the electrical connection is made by forming a through-hole of the through-via in advance in a process of forming the one flexible circuit board and the at least one other flexible circuit board, embedding the electrically-conductive material in the through-hole in a state in which the one flexible circuit board and the at least one other flexible circuit board overlap each other to form the through-via, and laying out in advance circuit interconnects on the one flexible circuit board and the at least one other circuit board so that parts of the circuit interconnects reach the regions in which the through-via is to be formed.
 5. The method for forming a laminated circuit board according to claim 4, wherein an opening of the through-via that is formed in the plurality of laminated circuit boards increases toward a top layer.
 6. The method for forming a laminated circuit board according to claim 1, wherein the plurality of flexible circuit boards are classified into two or more groups, a flexible circuit board lamination in which a plurality of flexible circuit boards are laminated is formed for each group, and the plurality of flexible circuit board laminations are laminated.
 7. The method for forming a laminated circuit board according to claim 1, wherein the electrical connection is made by forming a notch-shaped or semicircular recess in an end face of each of the flexible circuit boards, and arranging the electrically conductive material along the notch-shaped or semicircular recess to bring the electrically conductive material into contact with circuit interconnects formed on the flexible circuit boards. 